Attempts to synthesise quaternary MAX phases (Zr,M)2AlC and Zr2(Al,A)C as a way to approach Zr2AlC

Despite having never been synthesized, the MAX phase Zr2AlC attracts a lot of interest owing to its foreseen properties. A possible way to circumvent this obstacle is to stabilize Zr2AlC by partially substituting one of its constituting elements. Here we report on attempts to synthesise quaternary MAX phases (Zr,M)2AlC and Zr2(Al,A)C where M = Cr, Ti or Mo and A = S, As, Sn, Sb and Pb. We were notably able to produce Zr2(Al0.2Sn0.8)C, Zr2(Al0.35Pb0.65)C, and Zr2(Al0.3Sb0.7)C, with the latter representing the first antimony-based MAX phase ever reported

Improving the SLA-based management of QoS for secure multimedia services

This paper proposes to integrate security parameters into the Service Level Specification (SLS) template proposed in the Tequila project to improve SLA-based management of QoS [8], [21]. Integrating those parameters in the QoS part of the Service Level Agreement (SLA) specification is essential in particular for secure multimedia services since the QoS is negotiated when the multimedia service is deployed. Security mechanisms need to be negotiated at deployment time when sensible multimedia information is exchanged. In this paper we show that including security parameters in the SLA specification improves the SLA-based management of QoS and therefore the negotiation, deployment and use of the secure multimedia service. The parameters this paper proposes to integrate have the advantage to be understandable by both the end-users and service providers. © IFIP International Federation for Information Processing 2005

Mesurabilité des multiples dimensions de la communication interne

While the quantification of the reputation of brands and companies has developed since the 1990, internal communication was relatively untouched by this movement of evaluation and objectification of its effectiveness. For several years, we observe a resurgence of interest for this question of the measurement of the internal communication, as evidenced by recent research projects that have been conducted on the subject, but also the issues at the heart of the work of communication professionals. In this article, we propose to carry out a comparative analysis of the main studies and tools dealing with the question of the measurement of internal or organizational communication. Beforehand, we will build an analytical grid based on the multidimensional definition of internal communication. This comparative analysis of studies and tools for the assessment of the internal communication highlights the need to develop a new measurement approach. Finally, we will present our project of research-action which aims to create a multidimensional scale of measurement of internal communication.Alors que la quantification de la réputation des marques et des entreprises s’est développée depuis les années 1990, la communication interne fut jusqu’il y a peu relativement épargnée par ce mouvement d’évaluation et d’objectivation de son efficacité. Depuis plusieurs années, nous assistons toutefois à un regain d’intérêt pour cette question de la mesure de la communication interne. Dans le cadre de cet article, nous proposons de réaliser une analyse comparative des principales études et outils consacrés à cette question de la mesure de la communication interne ou organisationnelle. Au préalable, nous nous pencherons sur la construction d’une grille d’analyse s’appuyant sur la définition multidimensionnelle de la communication interne et une réflexion à propos de la mesure de chacune de ses dimensions. Cette analyse comparative des études et outils d’évaluation de la communication interne mettant en exergue la nécessité de développer une nouvelle approche de mesure, nous présenterons ensuite notre projet de recherche-action qui vise à créer une échelle de mesure multidimensionnelle de la communication interne.   &nbsp

Oxidation of UC: an in-situ high temperature environmental scanning electron microscopy study

Uranium carbide (UC) has the potential to be used as fuel in Generation IV nuclear reactors thanks to its higher metal atom density and better thermal conductivity when compared to the most commonly used fuel: uranium dioxide (UO2) [1]. Although UC offers improved properties during operation, it needs to be converted into an oxide form after usage as it is reactive and potentially pyrophoric [2] in oxidising environments. Previous oxidation studies on UC, performed over a range of oxygen atmospheres and temperatures, suggest different mechanisms lead to the formation of either a protective or a pulverised non-protective oxide layer [3]. New experimental observations of the oxidation and self-ignition of UC were reported in our previous work [4] involving a combination of state-of-the-art techniques: high temperature environmental scanning electron microscopy (HT-ESEM), high-resolution transmission electron microscopy (HRTEM) combined with an image analysis technique (ImageJ). In situ HT-ESEM oxidation of sintered UC fragments from 723 to 848 K in 10 to 100 Pa oxygen atmosphere revealed the morphological changes to the oxide during the transformations between UC to UO2 and UO2 to U3O8. Oxidation at 723 K in a low O2 atmosphere (≤ 25 Pa O2) produced a compact UO2+x oxide layer, confirmed by post mortem HRTEM analysis. The oxide formed after an induction period and it was accompanied by an exponential followed by logarithmic sample area expansion and crack propagation. Furthermore, samples oxidised at 50 Pa O2 at 723 K and at 773-848 K in an oxygen atmosphere of 10 to 100 Pa O2 showed “explosive” oxidation (see Figure 1). Sample expansion and crack propagation are well described by an exponential law until the “explosion” occurred causing a transformation to a popcorn-like morphology which is typical for oxidation from UO2 to U3O8. HRTEM analysis on the sample powder showed the oxide to be formed of a mixture of U3O7/U3O8 with U3O8 showing preferential growth in the [001] direction. The explosive nature of the oxide is triggered by ignition of UC, which set off this reaction throughout the entire sample with a propagation speed of 150-500 ± 50 µm/s, which shows similarities to a self-propagating high-temperature synthesis reaction. Please click Additional Files below to see the full abstract

Synthesis and physical properties of (Zr1−x,Tix)3AlC2MAX phases

MAX phase solid solutions physical and mechanical properties may be tuned via changes in composition, giving them a range of possible technical applications. In the present study, we extend the MAX phase family by synthesizing (Zr1−xTix)3AlC2 quaternary MAX phases and investigating their mechanical properties using density functional theory (DFT). The experimentally determined lattice parameters are in good agreement with the lattice parameters derived by DFT and deviate <0.5% from Vegard's law. Ti3AlC2 has a higher Vickers hardness as compared to Zr3AlC2, in agreement with the available experimental data

Experimental synthesis and density functional theory investigation of radiation tolerance of Zr3(Al1-xSix)C2 MAX phases

International audienceAbstractSynthesis, characterization and density functional theory calculations have been combined to examine the formation of the Zr3(Al1–xSix)C2 quaternary MAX phases and the intrinsic defect processes in Zr3AlC2 and Zr3SiC2. The MAX phase family is extended by demonstrating that Zr3(Al1–xSix)C2, and particularly compositions with x≈0.1, can be formed leading here to a yield of 59 wt%. It has been found that Zr3AlC2 ‐ and by extension Zr3(Al1–xSix)C2 ‐ formation rates benefit from the presence of traces of Si in the reactant mix, presumably through the in situ formation of ZrySiz phase(s) acting as a nucleation substrate for the MAX phase. To investigate the radiation tolerance of Zr3(Al1–xSix)C2, we have also considered the intrinsic defect properties of the end‐members. A‐element Frenkel reaction for both Zr3AlC2 (1.71 eV) and Zr3SiC2 (1.41 eV) phases are the lowest energy defect reactions. For comparison we consider the defect processes in Ti3AlC2 and Ti3SiC2 phases. It is concluded that Zr3AlC2 and Ti3AlC2 MAX phases are more radiation tolerant than Zr3SiC2 and Ti3SiC2, respectively. Their applicability as cladding materials for nuclear fuel is discussed.</jats:p

On the stoichiometry of zirconium carbide.

The dependencies of the enhanced thermomechanical properties of zirconium carbide (ZrCx) with sample purity and stoichiometry are still not understood due to discrepancies in the literature. Multiple researchers have recently reported a linear relation between the carbon to zirconium atomic ratio (C/Zr) and the lattice parameter, in contrast with a more established relationship that suggests that the lattice parameter value attains a maximum value at a C/Zr ~ 0.83. In this study, the relationship between C/Zr atomic ratio and the lattice parameter is critically assessed: it is found that recent studies reporting the thermophysical properties of ZrCx have unintentionally produced and characterised samples containing zirconium oxycarbide. To avoid such erroneous characterization of ZrCx thermophysical properties in the future, we propose a method for the accurate measurement of the stoichiometry of ZrCx using three independent experimental techniques, namely: elemental analysis, thermogravimetric analysis and nuclear magnetic resonance spectroscopy. Although a large scatter in the results (ΔC/Zr = 0.07) from these different techniques was found when used independently, when combining the techniques together consistent values of x in ZrCx were obtained